Split Injection

Split injection, or indirect sampling after vaporizing injection, was the earliest attempt to solve this problem. For many years it was the only technique available; it is still very popular.

Carrier flow through the injector is split; a small proportion is directed into the column and the remainder is vented. When the sample is vaporized a small proportion of the vapour cloud only is transferred to the column; this reduces the time during which sample is transferred into the column. The split ratio is:

carrier flow to atmosphere flow through the column

Most of sample is lost so the technique is not suitable for trace analysis (sample components present at levels below 0.01%) but it is well suited for complex, relatively low-boiling mixtures, such as gasoline, containing many components in the range 0.01-10%.

Originally it was widely believed that the splitter eliminated the column overloading believed to be responsible for excessive bandwidths. This could have been achieved by diluting the sample. Although the capacities of capillary columns are well below those of packed columns, the effect of overloading on band broadening is negligible compared with the effect of slow sample transfer.

Using eqn [1] for a 0.32 mm i.d. column with 90 000 theoretical plates and a component for which VR is 10 mL (elution after 5 min at 2mLmin~1)

shows that Vmax is approximately 1 |L (equivalent to 0.002 | L liquid). This formula gives a pessimistic result for capillary columns and 15 |L is more realistic. Even so, to reduce 0.5 mL vapour to 0.015 mL requires a split ratio of 33 : 1; to take account of sample diffusion in the carrier gas, practical split ratios must be considerably higher (> 100 : 1).

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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